Which of the Following Statements About Saliva Is NOT True

NST103 Spring2006 Name______KEY______SID______Midterm Exam I (5pages, 100pts)

I. (2pts each12pts) Choose the SINGLE best answer to each of the follwing questions:

1.Which of the following statements about saliva is NOT true? a. Water in saliva moistens food b. Glycoproteins in saliva lubricate and prevent abrasion c. Salivary sucrase initiates digestion of starch d. Antimicrobial agents reduce risk of infection Answer C .

2.Which of the following is absorbed primarily in the upper 40% of the small intestine? a. Cholic acid b. Vitamin B12 c. H2O d. Palmitic acid Answer D .

3.Which is NOT a function of the liver? a. Storage of bile salts b. Secretion of Bile salts c. Detoxification of urea d. Production of albumin Answer A .

4.Which of the following statements about the Unstirred Water Layer (UWL) is true? a. Movement through the UWL may be rate limiting for absorption of hydrophilic substances b. Rate of movement through the UWL is equivalent to the rate of movement through the membrane for hydrophobic compounds c. The UWL is in equilibrium with the lumen phase d. Rate of transport through the UWL is a function of concentration gradient for that substance and the diffusion coefficient for the substance

Answer D .

5.Which is not a function of non-digestible & non-absorbable carbohydrates? a. Aid elimination and reduce risk of diverticulosis b. May speed digestion and reduce risk of metabolic diseases c. May alter environment of colonic lumen and reduce risk of colonic diseases d. May increase satiety and reduce risk of overeating Answer B .

6. The lipoprotein attached to the chylomicron responsible for exocytosis is a. apoE b. apoB48 c. apoC d. apoB100 Answer __ B _

1 II. (4pts) Draw the chemical structures of the Fatty Acids 18:3 ω-3 and 18:3 Δ-9 1pt for total carbon number -1pt if structures are not the same 1pt for correct double bond number 1pt for correct double bond postion 1pt for COOH group

III. (5pts) Match the diseases on the left to their proper causes and/or symptoms on the right. You can use the same LETTER more than once. Put only ONE LETTER in each blank.

a. Celiac disease ___ B _ ___ defect in amino acid transporter b. Hartnup disease ____D____ insufficient pancreatic function c. Lactose intolerance ___ A/C__ causes diarrhea d. Type II diabetes ___ A_ systemic response to antigen ___ C_ insufficient amount of at least one brush border enzyme

IV. (1pt ea =4pts) How will transport change (indicate “increase” “decrease” “not change” or “stop”) under each of the following circumstances?

1.If sodium concentration inside the enterocyte increases, the rate of glucose transport into the enterocyte will decrease

2.If carbonic anhydrase activity inside the parietal cell is inhibited, Cl- secretion into the lumen will decrease

3.If GLUT2 activity in the enterocyte is inhibited, the rate of glucose transport into the cell will decrease

4. If a croissant is nicely browned, the absorption of the fat from that food will not change

V. (5pts) Match the compound (indicated by letter) to its response (indicated by number) by placing the corresponding letter in the blanks. Put only ONE LETTER in each blank.

A. CCK ____ D or C___ stimulates hydrochloric acid secretion B. Enterokinase ____ A__ stimulates liver to produce bile acids C. Gastrin ___ D or C___ activates pepsin D. Histamine ____ B__ stimulates lipid digestion E. Secretin ___ C___ causes pH in duodenum to be neutralized

IX. (8pts) Fill in the blanks.

1. Bile acids are formed in the ___liver_____ (name the organ). The precursor for bile acid production is __cholesterol__ (name the compound). Bile acids become associated with __Na___ and ____K____ to form bile salts, which then get associated with ___Taurine___ and ___Glysine__ to form conjugated bile salts. 2. The main products of dietary TAG digestion are MAG and FFA .

2 VII. (2 ea= 16pts) Determine whether each of the following statements is TRUE or FALSE. In either case briefly explain why. For any FALSE statements, make corrections and turn it into a true statement. 1pt for True/False 1pt for explanation 1. Blocking HCl production by the stomach would lead to a decrease in enzyme catalyzed CHO digestion in the stomach False. Blocking HCl production would lead to an increase in stomach pH, salivary amylase would not be denatured, therefore increased enzyme catalyzed digestion

2. Decreasing histidine consumption in the diet will result in increased stomach pH True. Histidine is the precursor to histamine, the action of which increases HCL production in the stomach, decreasing pH

3. A genetic mutation inactivating -dextrinase would not affect a person’s ability to digest amylopectin False. -dextrinase is required to hydrolyze the 6 bonds present in amylopectin. Without this enzyme, amylopectin digestion would be incomplete.

4. Carbohydrate and lipid digestion begins in the mouth. FALSE. Although carbohydrate digestion may begin in the mouth with salivary amylase, there are no lipase enzymes in saliva. Thus, lipid digestion begins in the stomach with the action of gastric lipase.

5. Methionine and proline are essential amino acids for humans FALSE. Proline is not an essential amino acid. Methionine is essential.

6. The same enzymes are required for digestion of both amylose and amylopectin FALSE. Common enzymes are salivary amylase, pancreatic amylase, glucoamylase and maltase. -dextrinase is required to hydrolyze the 6 bonds present in amylopectin.

7. When mixed micelles are endocytosed by enterocytes the lipids are absorbed FALSE mixed micelles are not endocytosed. Instead, the lipids contained in these micelles must diffuse out of the micelle to be absorbed.

8. For the absorption of amino acids, there are many different transporters. What purpose is served by this redundancy of function?

In case one fails the efficiency of AA uptake is not severely compromised since another transporter may perform the same function

3 VIII. (22pts) Fill in the blank with the appropriate word or phrase.

1 lysozyme Salivary component that causes lysis of microbial cell membranes

2 SGLT Na+-glucose symporter on apical membrane

3 lactoferrin Salivary agent that creates an iron deficient mileu

4 tight junctions Structure that eliminates intercellular space at apical end

5 sucrose Dimer of glucose and fructose

6 Ligament of Trietz Marks separation between duodenum and jejunum

7 Thoracic duct Site where lipid soluble compounds enter venous circulation

8 ____trypsin__ An enzyme that activates zymogens

9___pancreatic lipase______An enzyme which acts on either triacylglycerol or diacylglycerol.

10_____colipase______An enzyme that facilitates micelle formation

11____ Glut 2 or 5 Glucose uniporter on basolateral membrane of enterocytes

IX. (24pts) Provide brief answers to the following questions:

1. Why would the absence of ECL cells compromise HCL production in the stomach. No ECL  No histamine  no signal

2. Draw comparative plasma glucose concentration vs time curves for the 3hr period following consumption of two meals. Meal 1 contained 100g starch and Meal 2 contained 100g starch, 100 g protein, and 100g fat. Provide a justification for why these curves are the same or different.

Meal 1: Starch only The protein and fat in the mixed meal will dilute the proportion of energy that is from Meal 2: Mixed. carbohydrate. If the rate at which “energy” leaves the stomach is the same for both meals, then carbohydrate emptying rate is lower for Meal 2 than for Meal 2, causing carbohydrate absorption into the blood also to be lower..

3. What effect has FABP to fat absorption and why? It increases fat absorption since it reduces the intracellular concentration of FFA so that passive diffusion can still occur in terns of moving FFA from the lumen into the enterocytes

4 4. What is meant by the term Critical Micellar Concentration (CMC)? Use this term to explain how bile acid concentration in lumen affects fat absorption.

Concentration bile acids in the lumen must exceed CMC to form micellar structure. Dietary lipid can then diffuse into these bile acid micelles to form mixed micelles. Since micelles have greater affinity for an aqueous environment than do the lipid molecules themselves, the mixed micelles can more easily move through the unstirred water layer, delivering the lipid molecules to the apical membrane, and facilitating absorption.

5. Explain briefly how and why a genetic defect in enterokinase would influence the protein digestion. No enterokinase  no trypsin activation  no zymogens’ activation  no protein digestion

6. Describe how plasma glucose and insulin levels change as an individual moves from normo-glycemic to type 2 diabetic. Normal glucose normal insulin  normal glucose higher insulin  higher glucose higher insulin  high glucose high insulin  very high glucose insulin decreases